The invention relates to a cold-gas refrigerator comprising a working space which is formed inside a cylinder and in which a working medium performs a thermodynamic cycle; the said working space comprises a compression space of relatively higher mean temperature during operation and an expansion space of lower mean temperature during operation, said spaces communicating with each other via heat exchangers, including a regenerator. The working surface of a piston which is coupled to a drive varies the volume of the compression space during operation so as to generate pressure variations in the working medium, one working surface of a displacer which is reciprocatable at a phase difference with respect to the piston varying the volume of the expansion space, and the other working surface thereof varying the volume of the compression space in response to the said pressure variations.
A refrigerator of this kind is known from the article "Free displacer refrigeration" (Advances in Cryogenic Engineering, Volume 14, 1968, pages 361-369; Plenum Press-- New York 1969). In this known machine based on the Stirling cycle, the displacer is driven by the working medium itself while utilizing the flow loss of this medium in the regenerator. The regenerator may be accommodated in the displacer. The regenerator usually consists of a filling mass metal gauze layers or lead spheres, contained in a housing; however, the regenerator can alternatively be formed by an annular gap between the displacer and the enveloping cylinder wall (French Pat. specification No. 2,074,337, Canadian Pat. specification No. 921,716).
Besides a regenerator, the Stirling refrigerator also comprises other heat exchangers: namely a "freezer" between the expansion space and the regenerator, that is to say a heat exchanger in which expanded working medium can extract heat from an object to be cooled, while usually there is also a cooler present between the compression space and the regenerator in which compression heat can be extracted from the working medium.
The major advantage of this known refrigerator is its comparative simplicity because of the lack of mechanical drive provisions at the displacer. The drive of the piston is an important factor in the objective of further simplification and miniaturization, enhancement of the operating reliability and service life, reduction of the mechanical vibrations and of the noise level, and also in the attempts to reduce the cost price.
Various attempts have been made to replace the rotary drive, in which an electric motor drives the piston by way of a crank piston rod mechanism, by a simpler and cheaper system. For example, it is known from U.S. Pat. Nos. 3,220,201 and 3,765,187 to use a linear electromagnetic drive ("direct linear electromagnetic actuator" "solenoid drive linear motor") in Stirling refrigerators wherein an armature of a soft-magnetic material (soft-iron) reciprocates under the influence of a magnetic alternating field generated by an electromagnet. However, this does not result in a real structural simplification and cost price reduction of the refrigerator.
In addition, it is a known drawback of the electromagnetic drive (linear motor) that the attracting magnets of stator and armature and the unavoidable tolerances in the centering of the moving part of the machine, cause transverse forces which result in large friction losses, fast wear, noise and mechanical vibrations.
In order to balance the forces of inertia of the moving part, coiled springs are used. Because of the large overall mass of the soft-iron armature, the piston and the connection rod, the coiled springs should have a rather heavy construction and substantial rigidity. The spring characteristic varies in the course of time, and hence the efficiency of the machine. This necessitates periodical replacement of the springs.